Heretofore video processing systems for quantizing, encoding and otherwise preconditioning video signals, from whatever source, prior to transfer to and manipulation by digital computers have predominantly been of the genre classifiable as "frame grabbers". The operation of a frame grabber is such that each horizontal line is scanned by, for example, a video camera or similar transducer and analytically subdivided into, typically, several hundred picture elements, the picture elements commonly referred to as "pixels". The average brightness level of each pixel is represented by an analog voltage which is in turn quantized by an analog-to-digital converter (A/D) so as to render the gray scale level, a measure of the proportional brightness of that pixel, amenable to storage and processing via a computer.
Although offering a substantial amount of quantitive information regarding the image scanned by the video camera, the frame grabbing technique suffers as an inherently slow and expensive approach to video data acquistion. The drawback is largely attributable to the requirement to process approximately 10.sup.5 pixels per frame of video information. Relatively sophisticated and commensurately expensive hardware is required to digitally encode the analog signal representing the brightness level of each pixel and thereafter transfer into memory the information so encoded. Furthermore, the technique necessitates the use of a relatively powerful, in terms of both storage as well as a computational capacity, computer in order to process the video data so acquired in anything approaching real time applications.
U.S. patent application Ser. No. 548,112, filed Nov. 2, 1983 and entitled "Video Measurement System For Microcomputer", by the inventors of this invention, provides a substantially simplified approach to video data acquisition and, although not generally capable of delivering quite the level of quantitive information as the frame grabber described above, has proved entirely adequate in a broad range of applications involving dimensional measurements. For example, the system has proved quite useful in measuring the inside and outside diameters of quartz tubes in a production process.
The video processing system described in Ser. No. 548,112 is especially suited for use with microprocessors or microcomputers characterized by limited memory storage capacity and procesing capability. The video processing system includes a transition detector for detecting black-to-white and white-to-black transitions in a video signal, from whatever source. The output of the transition detector is coupled to a feature counter so that the feature counter provides at a computer buss an output indicative of the number of such transitions occurring during a particular horizontal scanning period. An output of the feature counter drives a decoder that selectively enables a plurality of feature timers, each of which has an input coupled to a clock so that the feature timers provide an output indicative of the time duration between successive transitions in the video signal. The video processing system thereby makes available to the microcomputer the number and respective durations of transitions during a horizontal scanning period. At the end of each horizontal line, this data is transferred via the computer buss into memory and the feature counter and feature timers are reset in preparation for the subsequent line. This cycle is repeated until an entire video frame has been encoded and transferred to the microcomputer for processing as desired.
To reiterate, the invention requires a modest amount of relatively less sophisticated circuitry in order to implement the interface of the video transducer (e.g., camera) to a computer. Furthermore, because the memory and computational demands are relaxed, it has been found possible to use relatively inexpensive microprocessors in real-time measurement and control applications otherwise requiring more sophisticated computers.
The subject invention may be deemed a functional and structural modification of the above in that the decoder is herein replaced by a shift register (SR). The SR is driven by the transition detector and is coupled to the feature timers so that the feature timers precisely measure the respective distances between the beginning of a line (i.e., left hand edge of a screen) and the occurrence of specified selected transitions. The distance between relevant transitions is therefore easily computed as needed.